According to the NPD, Mortal Kombat sold just under 900K copies. Portal 2, of course, came in at No. 2.
Likely as a result of these two games, total US spending was up 20 percent year-over year, from $802.4 million in 2010 to $961.2 million in 2011. Microsoft can also claim some responsibility for the high numbers -- it informed us that the Xbox 360 was the top-selling console last month, moving 297,000 units (a year-over-year increase of 60 percent).